This invention relates to medico-surgical instruments.
Various procedures and instruments are used to ventilate patients via the trachea. Tracheostomies can be made by a conventional surgical technique or by a percutaneous technique, which is quicker and more suited to emergency situations. In the usual percutaneous technique a needle is pushed through the skin of the throat into the trachea. Entry of the needle to the trachea is detected by a loss-of-resistance technique involving a syringe filled with air connected to the needle hub. The tip of the needle is blocked while it is passing through the neck tissue so that manual pressure applied to the needle plunger encounters a resistance to movement. When the tip of the needle enters the trachea air can flow and the plunger can move forwardly, enabling entry to be detected. The syringe is then removed and a guidewire is slid along the needle. The needle is then pulled out along the guidewire, leaving the guidewire in position. The opening into the trachea is then enlarged by sliding a dilator or a series of dilators of increasing size along the guidewire into the trachea. When the opening has been enlarged sufficiently, a tracheostomy tube is slid along the guidewire, following which the guidewire can be removed. Although the apparatus involved in this technique has been used successfully for many years, the number of different components and steps is not ideal for adverse situations, such as at the site of a trauma incident, and it may not be suitable for less experienced clinicians or paramedics.
An alternative technique used in emergency situations is percutaneous transtracheal ventilation. In this technique a sharp-tipped needle penetrates the trachea and the external, machine end of the needle is connected to a jet ventilation machine so that breathing gas is supplied to the trachea via the needle, which is left in position. This arrangement can be used to provide emergency ventilation for up to about one hour, which is usually sufficient time for the patient to be provided with alternative ventilation. The advantage of this procedure is that it can be carried out relatively easily by ambulance crew and paramedics and it does not involve the need for cutting with a scalpel. The procedure does, however, have several disadvantages. First, there is a risk that the needle will not be inserted to the correct depth, because of variations in thickness of neck tissue overlying the trachea. If the needle is not inserted far enough its tip may be located in the anterior tissues surrounding the trachea instead of in the trachea itself. If inserted too far, the needle may damage the posterior wall of the trachea. Second, because the ventilation gas emerges through the open tip of the needle and the bore of the needle is relatively small compared with a tracheal tube, the gas emerges as a jet directed longitudinally of the needle and towards the posterior wall of the trachea. Where the gas jet impinges on the tissue of the trachea it may cause drying and necrosis.
Another problem with emergency ventilation instruments is that it is usually necessary to hyperextend the neck in order to provide access to the trachea. Where the patient has suffered neck injury, or is suspected of having suffered a neck injury it is important that there is minimal movement of the neck. This is a particular disadvantage because patients requiring emergency ventilation are often those that have been involved in an accident of the kind that can cause neck injury.